Merge of the 'event-ide' branch. Hemlock's thread model has been changed
so that Hemlock commands now run in the Cocoa event thread -- see the
Hemlock file view.lisp for an overview.

IDE compilation has also been reorganized. Hemlock is now more fully
integrated into the IDE and cannot be compiled separately, sorry.

The hemlock-ext package has been repurposed to contain all interfaces
to window-system specific functionality.

There are also many many assorted other changes, cleanups and fixes.

The Hemlock documentation (Hemlock Command Implementor's Manual) in​http://trac.clozure.com/openmcl/wiki now correctly reflects the
implementation, although it doesn't (yet) describe the integration
with Cocoa or the threading model.